In typical storage systems, in order to prevent loss of data due to failures of storage apparatuses and the like, data backup processing is regularly performed. In such data backup processing, data stored in a data area of a master side at a certain point of time is copied into a data area of a backup side. However, when recovered, increasing of an amount of copying data to a great degree is likely to lead to increasing of an amount time necessary for the recovery to a great degree. Therefore, a backup management method, in which data backup timings are determined so that an amount of time necessary for recovery can be fallen within a specified period of time, has been disclosed (refer to Japanese Laid-open Patent Publication No. 2007-140700).
However, during a period of time while copying processing is performed, data updating is disabled, so that jobs are halted, and thus, technologies which make it possible to reduce the period of time while jobs are halted owing to the copying processing to a maximum extent, have been desired. Therefore, a system, in which, upon receipt of a copying request, by setting management information indicating completion or incompletion of copying for each unit data area resulting from segmentation of a data area targeted for copying, logical copying processing is completed, and afterward, copying of real data is processed, has been disclosed (refer to Japanese Patent No. 3606797). Such a system enables accessing for data subsequent to completion of the logical copying processing.
Further, nowadays, for the purpose of not only backup of data but also utilization of data in various applications, data copying processing between storage devices has been widely performed. For example, there is an application, in which a block of data stored in a storage apparatus providing a certain online service is copied to a system at a certain point of time, and then, batch processing on the copied block of data is performed by using the copy-destination system. Thus, not only unidirectional copying processing from a copy-source storage apparatus to a copy-destination storage apparatus, such as data backup processing, but also reverse directional copying processing, has become increasingly popular.
However, to date, there has been a disadvantage in that, regarding control methods, in each of which a copying process commences in response to a copying request, problems, such as data uncertainty, are likely to occur depending on statuses of copying processes in execution, and commands received thereunder.
As described above, data backup processing performed at predetermined backup timings causes a problem in that jobs are halted during a period of time while copying processing is performed, and thus, is undesirable. Therefore, it is desirable to perform copying processing upon occurrence of a copying request; however, as described above, since copying processes are performed in various applications, copying requests arise therefrom on an irregular basis. In particular, in existing copying processing methods, in order to reduce an amount of time necessary for copying, upon receipt of a copying request, by setting only management information, data accessing is permitted, and afterword, copying of real data is performed. Thus, it takes a certain period of time from reception of a copying request until completion of copying of real data. During this period of time, it is possible to receive other copying requests, and also make requests for cancelling copying processes in execution.
For example, during a period of time while a copying process for relevant data areas is being performed, for the same data areas as the relevant data areas, a copying execution command, in which a copy source of the copying process in execution is specified as a copy destination, and a copy destination of the copying process in execution is specified as a copy source, is likely to be inputted, and in response to the inputted copying execution command, a copying process is likely to start to be performed. Under such a condition, if commands for canceling both of the copying processes are inputted, data uncertainty is likely to arise in both a copy-source storage apparatus and a copy-destination storage apparatus. Therefore, depending on statuses of the copying processes in execution and commands received thereunder, from a viewpoint of system reliability, the statuses of the storage apparatuses are likely to transit to undesirable conditions.
However, in copying control methods employed by existing storage systems, processing have been performed so that copying commands are independently processed, and statues of other copying processes in execution, having been commenced by other copying commands and the like, are not taken into consideration. Consequently, it has been difficult to prevent such a storage system from falling in undesirable conditions.